Paper is ordinarily fed only in one direction in office machines such as copiers. Thus, in such office machines, a motor that rotates only in one direction is used. But in more sophisticated office machines having a paper feed station which allows paper to be selectively fed in either of forward and reverse directions, if a motor which rotates only in one direction is used, it is necessary to add a device for switching the rotational direction of the motor between forward and reverse rotational directions. (JP Patent Publication 5-307290A).
As a mechanism for switching driving force between forward and reverse directions, a known one shown in FIG. 18 includes three bevel gears (“Mechanical Movement Mechanism”, Gihodo Co., Ltd., published Oct. 15, 1957, page 81). This mechanism includes an input shaft 71, an input bevel gear 72 mounted on one end of the input shaft 71, an output shaft 73 extending perpendicular to the input shaft 71 and located close to the gear face of the input bevel gear 72, and a clutch 74 axially slidably keyed to the output shaft 73. On both sides of the clutch 74, a pair of output bevel gear portions 75 are rotatably mounted and mesh with the input bevel gear 72. On the respective opposed surfaces of the output bevel gear portions 75, bosses 76 are provided and each have teeth 77 configured to mesh with the clutch 74. The clutch 74 has a circumferential groove 78 in its central portion in which a pin 80 of a pivot arm 79 is inserted. The pivot arm 79 is pivotally mounted at its other end to a stationary portion by means of a shaft 81.
When the pivot arm 79 is inclined rightwardly or leftwardly, the clutch 74 axially slides and is brought into engagement with the teeth 77 of one of the output bevel gear portions 75. Thus, the rotation of the input shaft 71 is transmitted to the output shaft 73. When the pivot arm 79 is inclined in the opposite direction, the clutch 74 engages the other output bevel gear portion 75, and the output shaft 73 is rotated in the reverse direction.
With this switching device, because the input shaft 71 and the output shaft 73 extend perpendicular to each other, the positioning of a motor on the input side and paper feed rollers on the output side is restricted. Also, the input bevel gear has a large diameter, and the control mechanism for the pivot arm 79 is complicated in structure. Synchronizing means is also necessary to synchronize the angular phase of the teeth 77, thereby avoiding collision of teeth when the clutch 74 is switched over.